Cooling in a slip ring unit

Abstract

A slip ring unit for an electric generator is provided. The slip ring unit includes a slip ring attachable to a rotor shaft of the electric generator, a plurality of sliding contacts arranged along a circumference of the slip ring, to provide an electrical connection with the slip ring, at least one temperature sensor for measuring a temperature inside the slip ring unit, a fan for providing a cooling flow in the slip ring unit, and a controller connected to the fan for controlling the cooling flow rate generated by the fan, the controller being connected to the at least one temperature sensor. The at least one temperature sensor is attached to at least a holder for supporting the sliding contacts. The controller is configured in such a way that the cooling flow rate is generated depending on the temperature measured by the at least one temperature sensor.

1 . A slip ring unit for an electric generator comprising:
 a slip ring attachable to a rotor shaft of the electric generator;   a plurality of sliding contacts arranged along a circumference of the slip ring to provide an electrical connection with the slip ring;   at least one temperature sensor for measuring a temperature inside the slip ring unit,   at least one fan for providing a cooling flow in the slip ring unit, and   a controller connected to the at least one fan for controlling a cooling flow rate generated by the at least one fan, the controller being connected to the at least one temperature sensor,   wherein the at least one temperature sensor is attached to at least a holder for supporting the plurality of sliding contacts and the controller is configured in such a way that the cooling flow rate is generated depending on the temperature measured by the at least one temperature sensor.   
     
     
         2 . The slip ring unit according to  claim 1 , wherein the controller comprises an input for receiving a temperature signal from the at least one temperature sensor and an output for sending a controlling signal to the at least one fan, the controlling signal being a function of the temperature signal. 
     
     
         3 . The slip ring unit according to  claim 2 , wherein the controlling signal is proportional to the temperature signal. 
     
     
         4 . The slip ring unit according to  claim 3 , wherein the controlling signal is linearly proportional to the temperature signal. 
     
     
         5 . The slip ring unit according to  claim 2 , wherein the controlling signal is a voltage signal. 
     
     
         6 . An electric generator comprising a rotor, a stator, a rotor shaft and a slip ring unit according to  claim 1 . 
     
     
         7 . A wind turbine comprising an electric generator according to  claim 6 . 
     
     
         8 . An operating method for operating a slip ring unit according to  claim 1 ,
 the method comprising:   measuring a temperature inside the slip ring unit with the at least one temperature sensor,   providing a cooling flow in the slip ring unit, and   controlling the cooling flow rate depending on the temperature measured by the at least one temperature sensor.   
     
     
         9 . The operating method according to  claim 8 , wherein the cooling flow rate is proportional to the temperature signal. 
     
     
         10 . The operating method according to  claim 9 , wherein the cooling flow rate is linearly proportional to the temperature signal. 
     
     
         11 . The operating method according to  claim 8 , wherein the method further comprising:
 measuring a rotor speed and a rotor current;   calculating thermal losses in the slip ring unit;   calculating a required air flow in the slip ring unit depending on the thermal losses;   calculating a plurality of temperatures in a respective plurality of points of the slip ring unit,   determining at least one wear-ratio curve for the sliding contacts of the slip ring unit; and   determining an expected lifetime of the sliding contacts by using the at least one wear-ratio curve and the temperature measured inside the slip ring unit.